Communications between devices have been by and large specified by a number of standards organizations. These standards specify protocols which devices connected to a network must observe in order to communicate over the network. The standards also impose similar restraints on network components which interconnect the communication devices.
One standard, IEEE 802.2, specifies the protocols executed by the LLC layer. These protocols must be observed by the devices or users of the network. In turn the network components must also observe these same protocols as far as they can impact the user. In general the IEEE 802.2 standard (as well as others) assumes that a calling and a called station will be using separate LLC's (one associated with each user) interconnected by a transmission media.